Electroless Plating Pretreatment Agent and Copper-Clad Laminate for Flexible Substrate

ABSTRACT

Provided are an electroless plating pretreatment liquid used in a copper-clad laminate for a flexible substrate whose initial adhesive force between the substrate material and copper plating layer in an ordinary state as well as the adhesive force in a peel test after aging (in the atmosphere at 150° C. for 168 hours) are at least 0.4 kgf/cm, and a copper-clad laminate for a flexible substrate produced using same. The electroless plating pretreatment agent used in a substrate material of a copper-clad laminate for a flexible substrate comprising a thermoset resin and a silane coupling agent having a metal capturing capability. The copper-clad laminate for a flexible substrate wherein a substrate material is treated with the electroless plating pretreatment agent, a copper plating layer is then formed by electroless plating, and a copper plating layer is formed thereon by electroplating.

TECHNICAL FIELD

The present invention relates to an electroless plating pretreatmentagent used in materials of a copper-clad laminate used as a basematerial or the like of flexible substrates for printed wiring and to acopper-clad laminate for a flexible substrate produced using same.

BACKGROUND ART

Polyimide substrates are often used as a material of insulatingsubstrates for electronic components. With the recent trend towardsmaller, thinner electronics, two-layer copper polyimide substrates inwhich a metal layer is directly formed on a polyimide film haveattracted attention for their greater flexibility. Although the initialadhesive force of these substrates between polyimide films and metallayers in the ordinary state is on a practical level, thecharacteristics such as adhesive force in an environment requiring heatresistance, or in that of high temperature and high humidity areconsidered unstable.

A method for producing a metal layer in a flexible copper-clad laminateboard of polyimide film by sputtering is disclosed in Patent Document 1,for example. However, that method costs high, and the adhesive force isnot adequate in an environment requiring heat resistance, or anenvironment of high temperature and high humidity.

Methods to improve the adhesion of the polyimide film and metal layerinclude plasma, UV, and other dry processes as well as alkaline andother wet processes, but in addition to safety and operability issues ofthe liquid used, these methods can lead to unevenness in the metal layersurface if excessively applied, damaging fine wire formation.

Patent Document 2 describes a method of performing electrolytic copperplating after electroless copper plating comprising the five processesof forming a resin composite coating on a polyimide film, activating thecoating, applying a catalyst, activating the catalyst, and electrolessmetal plating. The main object of this method is to form a resincomposite layer as an adhesion imparting layer, but the processes arecomplex and results in a resin composite layer having a thickness of 1to 20 μm.

-   Patent Document 1: Japanese Patent Publication No. H9-136378-   Patent Document 2: Japanese Patent Publication No. 2001-168496

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an electrolessplating pretreatment liquid used in a copper-clad laminate for aflexible substrate whose initial adhesive force between the substratematerial and copper plating layer in an ordinary state, and the adhesiveforce in a peel test after aging (in the atmosphere at 150° C. for 168hours) are at least 0.4 kgf/cm, and a copper-clad laminate for aflexible substrate produced using same.

As a result of diligent investigations, the inventors have discovered asolution to the problems described above, that is, an electrolessplating pretreatment agent comprising a thermoset resin and a silanecoupling agent having a metal capturing capability is used as anelectroless plating pretreatment agent for the copper-clad laminate fora flexible substrate. A detailed description of the invention is asfollows.

(1) An electroless plating pretreatment agent applied to a substratematerial of a copper-clad laminate for a flexible substrate, comprisinga thermoset resin and a silane coupling agent having a metal capturingcapability.

(2) The electroless plating pretreatment agent according to (1), whereinsaid thermoset resin is an epoxy resin.

(3) A copper-clad laminate for a flexible substrate, wherein a substratematerial is treated with the electroless plating pretreatment agentaccording to (1) or (2), a copper plating layer is then formed byelectroless plating, and a copper plating layer is formed thereon byelectroplating.

EFFECT OF THE INVENTION

The copper-clad laminate for a flexible substrate, which is obtained bytreating a substrate material with an electroless plating pretreatmentagent of the present invention and then laminating an electroless copperplating layer and an electroplated copper layer, is a copper-cladlaminate for a flexible substrate having two copper layers excellent inadhesion such that the initial adhesive force between the substratematerial and copper plating layer in an ordinary state, and the adhesiveforce in a peel test after aging (in the atmosphere at 150° C. for 168hours) are at least 0.4 kgf/cm. An adhesive force is provided to thesurface of the substrate material without any wet or dry pretreatmentwhatsoever.

BEST MODE FOR CARRYING OUT THE INVENTION

The electroless plating pretreatment agent of the present inventioncomprises a thermoset resin and a silane coupling agent having a metalcapturing capability.

By adding the silane coupling agent having a metal capturing capability,a noble metal catalyst can be adhered to the surface to be plated moreuniformly and reliably via the silane coupling agent.

A preferred silane coupling agent is obtained by reacting an azolecompound or an amine compound with an epoxy compound.

Examples of the azole compound include imidazole, oxazole, thiazole,selenazole, pyrazol, isoxazole, isothiazole, triazole, oxadiazole,thiadiazole, tetrazole, oxatriazole, thiatriazole, bendazole, indazole,benzimidazole, and benzotriazole. While the azole compound is notlimited thereto, imidazole is especially preferred.

Examples of the amine compound include saturated hydrocarbon amines suchas propylamine, unsaturated hydrocarbon amines such as vinylamine, andaromatic amines such as phenylamine.

The silane coupling agent is a compound having an —SiX₁X₂X₃ group inaddition to having a noble metal capturing group derived from theabove-mentioned azole compound or amine compound, where X₁, X₂, and X₃represent an alkyl, halogen, alkoxide group or the like and may be afunctional group capable of being attached to an article to be plated.X₁, X₂, and X₃ may be identical or different.

The above-mentioned silane coupling agent may be obtained by reactingthe above-mentioned azole or amine compound with the epoxy silanecompound.

Such an epoxy silane compound is preferably an epoxy coupling agentexpressed as

(In the formula, R¹ and R² are hydrogen or alkyl groups having 1 to 3carbons, and n is a number from 0 to 3).

A reaction between the above-mentioned azole compound and theabove-mentioned epoxy group-containing silane compound is carried outunder the conditions described in Japanese Patent Publication No.H6-256358, for example.

For example, the above-mentioned silane coupling agent is obtained bydripping 0.1 to 10 mol of an epoxy group-containing silane compound in 1mol of an azole compound at 80 to 200° C. for between 5 minutes and 2hours. In that process, a solvent is not particularly needed, thoughchloroform, dioxane, methanol, ethanol, or some other organic solventmay be used.

An example of a particularly favorable reaction of an imidazole compoundwith an epoxy silane compound is shown below.

(In the formula, R¹ and R² indicate hydrogen or alkyl groups having 1 to3 carbons, R³ indicates hydrogen or an alkyl group having 1 to 20carbons, R⁴ indicates either an alkyl group having 1 to 5 carbons or avinyl group, and n indicates a number from 0 to 3.)

γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane,N-β(aminoethyl)γ-aminopropyltriethoxysilane, andγ-mercaptopropyltrimethoxysilane are other examples of silane couplingagents having a functional group with a metal capturing capability usedin the present invention.

As the thermoset resin used in the electroless plating pretreatmentagent of the present invention, epoxy resin, urea resin, phenol resin,melamine resin, and urethane resin are exemplified. By adding thethermoset resin, the adhesive force is improved. Using an epoxy resin asthe thermoset resin is preferable because it has a particularlyremarkable effect in improving the adhesive force.

It is not essential for the present invention that the electrolessplating pretreatment agent contains a noble metal compound. Platingactivity can be obtained by immersion in the plating pretreatment agentof the present invention and then in a palladium chloride aqueoussolution. Nevertheless, it is more preferable that the platingpretreatment agent contains a catalyst such as a noble metal compound.Examples of the catalyst include a compound of a noble metal such aspalladium, silver, platinum, or gold, for example a halide, a hydroxide,a sulfate and a carbonate thereof, and a noble metal soap thereof, ofwhich a palladium compound is particularly preferable. A conventionalcatalyst such as tin chloride may be contained in the platingpretreatment agent within the scope of the object of the presentinvention.

The noble metal soap can be obtained through a reaction of a fatty acid,a resin acid, or a naphthenic acid with a noble metal compound, and ispreferably used in the present invention.

For the fatty acid, the number of carbon atoms is preferably 5 to 25 andeven more preferably 8 to 16. If the number of carbons is 4 or less, thefatty acid does not dissolve readily in the organic solvent, causinginstability. With 26 or more carbon atoms, the portion soluble in theorganic solvent is limited and the noble metal content decreases,thereby the amount added is required to increase, which is notpractical.

Examples of the fatty acid include octylic acid, neodecanoic acid,dodecanoic acid, pentadecanoic acid, octadecanoic acid, and othersaturated fatty acids; oleic acid, linolic acid, and other unsaturatedfatty acids; hydroxytetradecanoic acid, carboxydecanoic acid, and otheroxygen-containing fatty acids; and mixtures thereof.

Preferable exemplifications of the fatty acids, resin acids, andnaphthenic acids include naphthenic acid, octylic acid, neodecanoicacid, and pentadecanoic acid.

Also, examples of the above-mentioned noble metal compound includecompounds that can form a soap with a fatty acid or the like, and thatcan be halides, hydroxides, sulfates, and carbonates of palladium,silver, platinum, and gold showing a catalytic effect when precipitatingcopper, nickel or the like on a surface of the material to be platedfrom an electroless plating solution, and palladium compounds areparticularly preferable among those compounds.

The noble metal soap used in the present invention can be obtained byordinary metal soap manufacturing method such as a direct method ordouble decomposition method with the above-mentioned fatty acid or thelike and the above-mentioned noble metal compound.

The palladium naphthenate preferred as the noble metal soap used in thepresent invention is shown below.

Mixture where n is from 9 to 13

Structural Formula of Palladium Naphthenate

The above-mentioned noble metal soap used in the present invention issoluble in organic solvents and stable as solution. Butanol,2-ethylhexanol, octyl alcohol, and other alcohols; xylene and otheraromatic hydrocarbons; hexane and other aliphatic hydrocarbons;chloroform; dioxane; and the like are examples of such an organicsolvent.

The electroless plating pretreatment agent of the present invention isused by dissolving the silane coupling agent having a metal capturingcapability, thermoset resin, noble metal soap and the like in an organicsolvent such as butanol, 2-ethylhexanol, octyl alcohol, or another suchalcohol; xylene or another such aromatic hydrocarbon; hexane or anothersuch aliphatic hydrocarbon; chloroform; or dioxane; for example.

Although the concentration of the silane coupling agent having a metalcapturing capability in the electroless plating pretreatment agent ispreferably 0.001 to 10 wt % and more preferably 0.05 to 3 wt %, it isnot limited thereto. If the concentration is less than 0.001 wt %, thequantity of the compound that attaches to the surface of the substratematerial is too low, and the effects are difficult to achieve. If itexceeds 10 wt %, too much compound attaches, thereby drying is difficultand powder readily aggregates.

The concentration of thermoset resin in the electroless platingpretreatment agent is preferably 0.001 to 30 wt %, and more preferably0.05 to 10 wt %. If it is less than 0.001 wt %, there is little effect,and if it exceeds 30 wt %, the liquid viscosity is too high, resultingin unevenness in the plating.

The noble metal soap may be used in the solution of the electrolessplating pretreatment agent at a noble metal concentration of 1 to 30,000mg/L or preferably 50 to 10,000 mg/L.

Various types of polyimide films, PET, and the like are preferably usedas the substrate material of the copper-clad laminate for a flexiblesubstrate of the present invention. Kapton (manufactured byToray-DuPont) and UPILEX (manufactured by Ube Industries) are examplesof the polyimide film, and Lumirror (manufactured by Toray Industries)is an example of the PET.

Although a method such as immersion, brushing, or spin coating istypically used to treat the substrate material with the electrolessplating pretreatment agent, the treatment method is not limited thereto,and any method resulting in a pretreatment agent applying to the surfaceis fine.

In order to volatize the used solvent after surface treatment, heatingthe solvent to at least the volatilization temperature thereof and thendrying the surface are enough, but it is preferable to further heat for3 to 60 minutes at 60 to 120° C.

The thickness of an electroless plating pretreatment agent layer of thepresent invention is preferably 1 to 200 nm.

The copper-clad laminate for a flexible substrate of the presentinvention is made by forming a copper plating layer by ordinaryelectroless plating on a substrate material pretreated as describedabove, and then further forming a copper plating layer by ordinaryelectroplating. In this manner, a copper-clad laminate for a flexiblesubstrate that is uniform and is excellent in adhesion is obtained.

The present invention is described in detail with reference to examples.

EXAMPLE 1

An electroless plating pretreatment agent with an organic solvent(butanol) including 1 g/L of imidazole silane (an equimolar reactionproduct of imidazole and 3-glycidoxypropyltrimethoxysilane), 0.5 g/L(100 mg/L of palladium) of palladium soap (palladium naphthenate,manufactured by Nikko Materials), and 1 g/L of epoxy resin (EpicoatEP828, manufactured by Japan Epoxy Resins) was applied to the surface ofthe commercially available polyimide film Kapton (200H, manufactured byToray-DuPont). After removing the solvent at 150° C. and forming apretreatment agent layer having a thickness of 70 nm, a copper platinglayer having a thickness of 0.5 μm was formed by electroless copperplating (plating solution: NKM554, manufactured by Nikko Metal Plating),and electric copper plating (plating solution: copper sulfate base,manufactured by Nikko Metal Plating) was carried out with a currentdensity of 2 A/dm² to form a copper plating layer having a thickness of35 μm. The peeling strengths were measured in an ordinary state and thenafter aging for 168 hours at 150° C. in the air. The peeling strengthswere measured by a 90-degree peeling test according to JIS C-6481. Thesame testing method was used in the below examples and comparativeexamples. The results showed a high post-aging strength of 0.7 kgf/cm asin Table 1.

EXAMPLE 2

An electroless plating pretreatment agent with an organic solvent(butanol) including 1 g/L of imidazole silane (an equimolar reactionproduct of imidazole and 3-glycidoxypropyltrimethoxysilane), 0.5 g/L(100 mg/L of palladium) of palladium soap (palladium naphthenate,manufactured by Nikko Materials), and 2 g/L of phenol resin (XLC-4L,manufactured by Mitsui Chemicals) was applied to the surface of thecommercially available polyimide film Kapton (200H, manufactured byToray-DuPont). After removing the solvent at 150° C. and forming apretreatment agent layer having a thickness of 70 nm, a copper platinglayer having a thickness of 0.5 μm was formed by electroless copperplating (plating solution: NKM554, manufactured by Nikko Metal Plating),and electric copper plating (plating solution: copper sulfate base,manufactured by Nikko Metal Plating) was carried out to form a copperplating layer having a thickness of 35 μm. The peeling strengths in anordinary state and after aging for 168 hours at 150° C. in the air weremeasured.

EXAMPLE 3

Treatment and testing were carried out in the same manner as in Example1 except that aminosilane (γ-aminopropyltriethoxysilane, manufactured byShin-Etsu Chemical) was used in place of the imidazole silane inExample 1. The results showed a high post-aging strength of 0.4 kgf/cmas in Table 1.

COMPARATIVE EXAMPLE 1

Treatment and testing were carried out in the same manner as in Example1 except that no epoxy resin was used. As shown in Table 1, the resultsshowed a high initial peeling strength of 0.9 kgf/cm, but a lowpost-aging peeling strength of 0.1 kgf/cm.

COMPARATIVE EXAMPLE 2

After forming a copper seed layer having a thickness of 0.5 μm bysputtering, 35 μm of copper plating layer was formed by electric copperplating in the same manner as Example 1, and testing was carried out asin Example 1. The results are shown in Table 1, with the initial peelingstrength high at 0.9 kgf/cm, though low after aging. TABLE 1 Peelingstrength in Initial peeling peel test after strength (kgf/cm) aging(kgf/cm) Example 1 0.9 0.7 Example 2 0.8 0.6 Example 3 0.6 0.4Comparative 0.9 0.1 Example 1 Comparative 0.9 0.1 Example 2

1. An electroless plating pretreatment agent applied to a substratematerial of a copper-clad laminate for a flexible substrate, comprisinga thermoset resin and a silane coupling agent having a metal capturingcapability.
 2. An electroless plating pretreatment agent according toclaim 1, wherein said thermoset resin is an epoxy resin.
 3. Acopper-clad laminate for a flexible substrate, wherein a substratematerial is treated with the electroless plating pretreatment agentaccording to claim 1, a copper plating layer is then formed byelectroless plating, and a copper plating layer is formed thereon byelectroplating.